Catalyst for producing isobutylene and method for producing isobutylene using the same

ABSTRACT

Provided are a catalyst whereby isobutylene can be produced at high yield in a lower-temperature environment, and a method for producing isobutylene using the catalyst. The catalyst for producing isobutylene is an oxide including at least one element selected from molybdenum and tungsten, and at least one element selected from tantalum, niobium, and titanium.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 14/416,924, filed on Jan. 23, 2015, which is a 35 U.S.C. §371national stage patent application of international patent applicationPCT/JP2013/075130, filed on Sep. 18, 2013, which claims priority toJapanese patent application JP 2012-204035, filed on Sep. 18, 2012.

TECHNICAL FIELD

The present invention relates to a catalyst for producing isobutyleneand a method for producing isobutylene using the same.

BACKGROUND ART

The majority of chemical products are manufactured using petroleum as araw material. In recent years, however, the depletion of petroleum isconcerned and carbon dioxide generated at the time of burning petroleumis considered as a cause of global warming. Hence, biomass-derivedchemicals called carbon neutral are expected as a substitute ofpetroleum.

Isobutylene is one of important chemical raw materials which areconverted into ethyl tert-butyl ether (ETBE), p-xylene, methylmethacrylate (MMA) and the like.

Isobutanol is produced as a byproduct at the time of producing2-ethylhexanol by oxo reaction using water gas and propylene as rawmaterials.

On the other hand, isobutanol is known to be produced by thefermentation of glucose and exemplified as one of the biomass-derivedraw materials. For example, it is described in Non-Patent Literature 1and Patent Literature 1 that isobutylene can be produced by thedehydration of isobutanol.

CITATION LIST Patent Literature

-   Patent Literature 1: JP 11-514337 W

Non-Patent Literature

-   Non-Patent Literature: Topics in Catalysis (2010) 53, 1224-1230

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

The above-mentioned reaction is an endothermic reaction since it is adehydration reaction, and thus the reaction requires more thermal energyin the case of being conducted in a high temperature region. A reactionin a lower temperature region is desired in order to cut down the amountof thermal energy used from the viewpoint of energy saving. InNon-Patent Literature 1, it is required to set the reaction temperatureto 300° C. in order to achieve a high conversion rate although γ-aluminais used as a catalyst and thus selectivity is high. In Patent Literature1, the development of catalyst is desired which can achieve a highconversion rate at a lower temperature and high selectivity althoughniobic acid and silica alumina are used as a catalyst and thus thereaction temperature required to achieve a high conversion rate is lowerthan the case of using γ-alumina.

The invention is made to solve the above-mentioned problem. In otherwords, an object of the invention is to provide a catalyst which canproduce a high yield of isobutylene in a lower temperature region and amethod for producing isobutylene using the same.

Means for Solving Problem

A catalyst for producing isobutylene according to the invention is anoxide containing at least one element selected from a group A and atleast one element selected from a group B, and the group A hereinconsists of molybdenum and tungsten and preferably tungsten and thegroup B herein consists of tantalum, niobium, and titanium. The oxide ispreferably a complex oxide. Moreover, a ratio (A/B) of a total A of thenumbers of moles of molybdenum and tungsten to a total B of the numbersof moles of tantalum, niobium, and titanium is preferably from 0.1 to10.

Effect of the Invention

According to the invention, it is possible to provide a catalyst whichcan produce a high yield of isobutylene in a lower temperature regionand a method for producing isobutylene using the same.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a schematic diagram illustrating an example of a reactionapparatus used in a liquid phase reaction.

MODE(S) FOR CARRYING OUT THE INVENTION

The catalyst for producing isobutylene according to the invention is anoxide containing at least one element selected from a group A and atleast one element selected from a group B.

Group A: molybdenum and tungsten

Group B: tantalum, niobium, and titanium

The catalyst for producing isobutylene according to the invention can beused as a catalyst, for example, in the method for producing isobutyleneby the dehydration of isobutanol.

The catalyst according to the invention is an oxide containing one ormore elements selected from molybdenum and tungsten and one or moreelements selected from tantalum, niobium, and titanium. It is presumedthat the one or more elements selected from molybdenum and tungsten havea function to form the backbone of the catalyst structure and the one ormore elements selected from tantalum, niobium, and titanium have afunction to form the active site structure. By virtue of this, it ispossible to produce a high yield of isobutylene even in a lowertemperature region, for example, in the case of producing isobutylene bythe dehydration of isobutanol using the catalyst described above.

Tungsten is preferred between molybdenum and tungsten since the activityis more improved.

The element ratio ((Mo+W)/(Ta+Nb+Ti)) of one or more elements selectedfrom molybdenum and tungsten to one or more elements selected fromtantalum, niobium, and titanium which are contained in the oxide is notparticularly limited but is preferably 0.01 or more and 10 or less. Theoptimal element ratio is different depending on the combination of theelements to be used and, for example, the element ratio (Mo+W)/Ta ismore preferably 1.0 or more and 9.0 or less. The element ratio (Mo+W)/Nbis more preferably 0.25 or more and 4.0 or less. The element ratio(Mo+W)/Ti is more preferably 2.0 or more and 8.0 or less. The catalyticactivity becomes more favorable when the element ratio((Mo+W)/(Ta+Nb+Ti)) is within the above range. Meanwhile, it ispreferable that the element ratio be within the above range even in acase in which the oxide contains only either of molybdenum or tungstenand/or only one of tantalum, niobium, and titanium. It is preferablethat the element ratio (W/Ta) be within the above range, for example,even in a case in which the oxide contains tungsten and tantalum butdoes not contain molybdenum, niobium, and titanium. In addition, theabove element ratio is a value calculated from the amount of each of theelements charged as the raw materials.

The oxide containing one or more elements selected from molybdenum andtungsten and one or more elements selected from tantalum, niobium, andtitanium may be a complex oxide of the respective elements or a mixtureof oxides of the respective elements. However, the oxide is preferably acomplex oxide of the respective elements. Meanwhile, it is possible toconfirm that the oxide is a complex oxide of the respective elements byX-ray diffraction.

In the complex oxide constituted by one or more elements selected frommolybdenum and tungsten and one or more elements selected from tantalum,niobium, and titanium, oxygen which is a constituent of the complexoxide is present at the atomic ratio of oxygen required to satisfy thevalence of each component.

The catalyst according to the invention may be supported on a support.The support is not particularly limited, and examples thereof mayinclude alumina, silica, silica alumina, titania, and zirconia. Only onekind of these may be used, or two or more kinds thereof may be usedconcurrently.

Hereinafter, an example of a method for producing the catalyst accordingto the invention will be described.

It is possible to use an oxide, a sulfate salt, a nitrate salt, acarbonate salt, an oxalate salt, a hydroxide, an ammonium salt, anorganic acid salt, a halide and the like of each of the elements as theraw materials of the catalyst components. It is possible to use, forexample, ammonium paramolybdate and molybdenum trioxide as themolybdenum raw material. It is possible to use, for example, ammoniumparatungstate and ammonium metatungstate as the tungsten raw material.It is possible to use, for example, tantalum acid as the tantalum rawmaterial. It is possible to use, for example, niobic acid, niobiumhydrogen oxalate, and ammonium niobium oxalate as the niobium rawmaterial. It is possible to use, for example, titanium (III) sulfate asthe titanium raw material. Only one kind of the raw materials of thecatalyst components may be used for each element or two or more kindsthereof may be used in combination.

These raw materials are dissolved or dispersed in a liquid. It ispossible to use water, an organic solvent such as alcohols such asmethanol, ethanol, 2-propanol, and the like as the liquid. Only one kindof these liquids may be used or two or more kinds thereof may be usedconcurrently.

The hydrothermal synthesis is performed using the solution or dispersionthus obtained. The hydrothermal synthesis can be conducted in anautoclave. The temperature for hydrothermal synthesis is preferably 125°C. or higher and 300° C. or lower, more preferably 150° C. or higher and250° C. or lower, and even more preferably 175° C. or higher and 230° C.or lower. The solid matter obtained by the hydrothermal synthesis ispreferably washed with water, an organic solvent or the like in order toremove undesired dissolved components. After the washing, filtering isperformed in order to separate the solid matter from the solvent.

Thereafter, the solid matter thus obtained is subjected to the heattreatment. The atmosphere gas used in the heat treatment is notparticularly limited, and it is possible to use, for example, air,nitrogen, argon, carbon dioxide, and steam. Only one kind of theseatmosphere gases may be used or two or more kinds thereof may be usedconcurrently. The temperature for heat treatment is preferably 300° C.or higher and 1000° C. or lower, more preferably 400° C. or higher and800° C. or lower, and even more preferably 500° C. or higher and 700° C.or lower. The time for heat treatment is preferably 10 minutes or longerand 10 hours or shorter, more preferably 30 minutes or longer and 5hours or shorter, and even more preferably 1 hour or longer and 2 hoursor shorter. In this manner, it is possible to obtain a catalyst.

The catalyst thus obtained can be molded if necessary and then used. Asa method for molding the catalyst, for example, a method is exemplifiedin which an additive is mixed with the catalyst if necessary, and thenthe mixture is molded into an arbitrary shape such as a spherical shape,a ring shape, a cylindrical shape, or a star shape using a powdermolding machine such as a tablet molding machine, an extrusion moldingmachine, or a tumbling granulator. In addition, the catalyst thusobtained may be ground to be used as powder.

Next, a method for producing isobutylene from isobutanol using thecatalyst described above will be described. The method for producingisobutylene according to the invention is a method for producingisobutylene by the dehydration of isobutanol and uses the catalyst forproducing isobutylene described above.

Isobutylene can be produced, for example, by bringing gaseousisobutanol, which is a raw material, into the gas phase contact with thecatalyst described above in an inert gas stream so as to dehydrate.

It is preferable to use biomass-derived isobutanol as isobutanol of theraw material from the viewpoint of environmental protection. Examples ofthe biomass-derived isobutanol may include isobutanol obtainable by thefermentation of glucose.

The concentration of isobutanol which is the reaction raw material inthe source gas can be freely selected. It is possible to use nitrogen,carbon dioxide, steam, or the like as the inert gas. Only one kind ofthese inert gases may be used or two or more kinds thereof may be usedconcurrently. The reaction pressure is preferably from the normalpressure to 1 MPaG and more preferably from the normal pressure to 0.5MPaG. The reaction temperature can be selected in the range of from 100to 400° C. but is preferably from 100 to 250° C., more preferably from100 to 200° C., and even more preferably from 100 to 150° C. from theviewpoint of sufficiently obtaining the effect of the invention.

On the other hand, it is also possible to produce isobutylene by thedehydration of liquid isobutanol through the liquid phase reaction.Isobutanol which is the reaction raw material in the liquid phase rawmaterial can also be diluted with an appropriate solvent, but thereaction may be conducted using 100% by mass of isobutanol withoutdiluting. An organic solvent may be used for the concentrationadjustment of isobutanol. In addition, an inert gas may be supplied inorder to remove oxygen, and it is possible to use nitrogen, carbondioxide, or the like. The reaction pressure is not particularly limitedbut is preferably from the reduced pressure to 1 MPaG and morepreferably from −0.001 MPaG to 0.5 MPaG. The reaction temperature can beselected from the boiling point of isobutanol or lower but is preferablynear the boiling point from the viewpoint of improving the activity.

EXAMPLES

Hereinafter, the invention will be specifically described with referenceto Examples on the dehydration of isobutanol, but the invention is notlimited to these Examples.

The analyses of the source gas and the product were performed using thegas chromatography. Meanwhile, the conversion rate of isobutanol and theselectivity and yield of isobutylene to be produced are defined asfollows.

Conversion rate of isobutanol (%)=(β/α)×100

Selectivity of isobutylene (%)=(γ/δ)×100

Yield of isobutylene (%)=(β/α)×(γ/δ)×100

Decomposition speed of isobutanol (mmol/h·g)=δ/(a×b)

Here, α denotes the number of moles of isobutanol supplied, β denotesthe number of moles of isobutanol reacted, γ denotes the number of molesof isobutylene produced. In addition, δ denotes the number of moles ofthe total reaction products (isobutylene, 1-butene, cis-2-butene,trans-2-butene and n-butane) detected by the gas chromatography. Inaddition, a denotes the reaction time (h), and b denotes the amount ofcatalyst (g).

Example 1

The solution prepared by dissolving 2.0 mmol of ammonium metatungstateas tungsten in 20 ml of water and the dispersion prepared by dispersing2.0 mmol of tantalic acid as tantalum in 25 ml of water were introducedinto an autoclave and subjected to the hydrothermal synthesis at 175° C.for 72 hours. This was filtered, and the solid substance was subjectedto the heat treatment at 500° C. for 2 hours under a nitrogen gas streamso as to prepare a catalyst.

The catalyst thus obtained was ground to obtain a powder. Quartz sandwas added to 0.2 g of the powder so as to have a volume of 4 ml, andthen the resultant was packed in a reactor having an inner diameter of12.8 mm. As the material gas, nitrogen and isobutanol (as gas) wereallowed to flow at 20 mol/min and 0.304 ml/min, respectively, andallowed to react at a reaction temperature of 150° C. The results arepresented in Table 1.

Example 2

The same operation as in Example 1 was conducted except using thesolution prepared by dissolving 2.7 mmol of ammonium metatungstate astungsten in 20 ml of water. The results are presented in Table 1.

Example 3

The same operation as in Example 1 was conducted except using thesolution prepared by dissolving 6.0 mmol of ammonium metatungstate astungsten in 20 ml of water. The results are presented in Table 1.

Example 4

The same operation as in Example 1 was conducted except using thesolution prepared by dissolving 2.7 mmol of ammonium paramolybdateinstead of ammonium metatungstate as molybdenum in 20 ml of water. Theresults are presented in Table 1.

Example 5

The solution prepared by dissolving 0.5 mmol of ammonium paramolybdateinstead of ammonium metatungstate as molybdenum in 20 ml of water wasused. In addition, the dispersion prepared by dispersing 2.0 mmol ofammonium niobium oxalate instead of tantalic acid as niobium in 20 ml ofwater was used. The same operation as in Example 1 was conducted exceptthese operations. The results are presented in Table 1.

Example 6

The solution prepared by dissolving 5.0 mmol of ammonium metatungstateas tungsten in 20 ml of water, the dispersion prepared by dispersing0.814 mmol of titanium (III) sulfate as titanium in 25 ml of water, andfurther 5 mmol of oxalic acid were introduced into an autoclave andsubjected to the hydrothermal synthesis at 175° C. for 24 hours. Thiswas filtered, and the solid substance was subjected to the heattreatment at 500° C. for 2 hours under a nitrogen gas stream so as toprepare a catalyst. The same operation as in Example 1 was conductedexcept those operations. The results are presented in Table 1.

Comparative Example 1

The same operation as in Example 1 was conducted except using γ-alumina(trade name: AL3996 manufactured by BASF) as the catalyst. The resultsare presented in Table 1.

Comparative Example 2

The same operation as in Example 1 was conducted except using tantalicacid as the catalyst. The results are presented in Table 1.

Comparative Example 3

The same operation as in Example 1 was conducted except using niobicacid as the catalyst. The results are presented in Table 1.

[Table 1]

TABLE 1 Elapsed reaction Conversion Selectivity Yield Catalyst time (hr)rate (%) (%) (%) Example 1 WTaO (W/Ta = 1) 3.5 100.0 89.6 89.6 Example 2WTaO (W/Ta = 1.35) 2.8 76.3 80.1 61.1 Example 3 WTaO (W/Ta = 3) 3.8100.0 87.0 87.0 Example 4 MoTaO (Mo/Ta = 1.35) 2.5 10.6 90.7 9.6 Example5 MoNbO (Mo/Nb = 0.25) 2.5 28.8 81.8 23.6 Example 6 WTiO (W/Ti = 6.14)5.0 100.0 82.5 82.5 Comparative γ-alumina 2.6 0.0 — 0.0 Example 1Comparative Tantalic acid 1.5 4.3 82.1 3.5 Example 2 Comparative Niobicacid 1.5 1.2 61.2 0.7 Example 3

Example 7

As illustrated in FIG. 1, 20 ml of isobutanol was introduced into athree-necked flask 1, a condenser tube 2, a thermometer 3, and anitrogen introduction line 4 were provided thereto, a nitrogen gas wasallowed to flow into the flask at 20 ml/min, and the temperature insidethe flask was raised to 105° C. under a normal pressure. To the flask,0.2 g of the catalyst prepared in Example 6 was added and the reactionwas conducted for 5 hours. The gas at the outlet of the condenser tubewas analyzed. The results are presented in Table 2.

Example 8

The same operation as in Example 7 was conducted except using thecatalyst prepared in Example 1. The results are presented in Table 2.

Comparative Example 4

The same operation as in Example 7 was conducted except using thecatalyst used in Comparative Example 1. The results are presented inTable 2.

[Table 2]

TABLE 2 Decomposition speed Selectivity Catalyst (mmol/h · g) (%)Example 7 WTiO (W/Ti = 6.14) 0.337 89.4 Example 8 WTaO (W/Ta = 1) 0.02786.9 Comparative γ-alumina 0.000 — Example 4

As presented in Table 1, it was possible to obtain a high yield ofisobutylene even by the reaction in a low temperature region of 150° C.in Examples.

As presented in Table 2, it was possible to obtain isobutylene even bythe reaction in a low temperature region of 105° C. in Examples.

According to the invention, it is possible to provide a catalyst whichcan produce a high yield of isobutylene in a lower temperature region.

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2012-204035, filed on Sep. 18,2012, the entire contents of which are incorporated herein by reference.

Hereinbefore, the invention has been described with reference toembodiments and Examples, but the invention is not intended to belimited to the above embodiments and Examples. It should be understoodby those skilled in the art that various modifications could be made tothe configuration and details of the invention without departing fromthe scope of the invention.

The invention claimed is:
 1. A method for producing isobutylene,comprising: dehydrating isobutanol in the presence of a catalyst,wherein the catalyst is a complex oxide comprising: (a) at least oneelement selected from the group consisting of molybdenum and tungsten;and (b) at least one element selected from the group consisting oftantalum, niobium, and titanium.
 2. The method according to claim 1,wherein the dehydrating comprises bringing a gaseous isobutanol intocontact with the catalyst.
 3. The method according to claim 1, whereinthe dehydrating comprises bringing a liquid isobutanol into contact withthe catalyst.
 4. The method according to claim 1, wherein the isobutanolis a biomass-derived isobutanol.
 5. The method according to claim 1,wherein a ratio (A/B) of a total A of the numbers of moles of molybdenumand tungsten to a total B of the numbers of moles of tantalum, niobium,and titanium is from 0.1 to
 10. 6. The method according to claim 1,wherein the catalyst is supported on a support.
 7. The method accordingto claim 1, wherein the catalyst comprises tungsten and tantalum.
 8. Themethod according to claim 7, wherein the catalyst consists of a complexoxide of tungsten and tantalum.
 9. The method according to claim 1,wherein the catalyst comprises molybdenum and tantalum.
 10. The methodaccording to claim 9, wherein the catalyst consists of a complex oxideof molybdenum and tantalum.
 11. The method according to claim 1, whereinthe catalyst comprises molybdenum and niobium.
 12. The method accordingto claim 11, wherein the catalyst consists of a complex oxide ofmolybdenum and niobium.
 13. The method according to claim 1, wherein thecatalyst comprises tungsten and titanium.
 14. The method according toclaim 13, wherein the catalyst consists of a complex oxide of tungstenand titanium.
 15. The method according to claim 1, wherein the catalystconsists of a complex oxide of molybdenum, tungsten, and tantalum, andwherein the element ratio (Mo+W)/Ta in said catalyst is 1.0 or more and9.0 or less.
 16. The method according to claim 1, wherein the catalystconsists of a complex oxide of molybdenum, tungsten, and niobium, andwherein the element ratio (Mo+W)/Nb in said catalyst is 0.25 or more and4.0 or less.
 17. The method according to claim 1, wherein the catalystconsists of a complex oxide of molybdenum, tungsten, and titanium, andwherein the element ratio (Mo+W)/Ti in said catalyst is 2.0 or more and8.0 or less.
 18. The method according to claim 1, wherein the catalystconsists of a complex oxide of tungsten and at least one elementselected from tantalum, niobium, and titanium.
 19. The method accordingto claim 1, wherein the catalyst consists of a complex oxide ofmolybdenum and at least one element selected from tantalum, niobium, andtitanium.